The catalytic preparation of hydrocarbons from synthesis gas, i.e. a mixture of carbon monoxide and hydrogen, is well known in the art and is commonly referred to as Fischer-Tropsch synthesis.
Catalysts suitable for use in a Fischer-Tropsch synthesis process typically contain a catalytically active metal of group 8, 9 or 10 of the Periodic Table of the Elements (Handbook of Chemistry and Physics, 89th edition, CRC Press, 2008-2009) supported on a refractory oxide, such as alumina, titania, zirconia, silica or mixtures of such oxides. In particular, iron, nickel, cobalt and ruthenium are well known catalytically active metals for such catalysts. Reference may be made to EP-A-398420, EP-A-178008, EP-A-167215, EP-A-168894, EP-A-363537, EP-A-498976 and EP-A-71770, optionally in combination with one or more metal oxides and/or metals as promoters selected from zirconium, titanium, chromium, vanadium and manganese, especially manganese. Such catalysts are known in the art and have been described for example, in the specifications of WO 9700231A and U.S. Pat. No. 4,595,703. CN 104 174 400, US 2012/083540, U.S. Pat. No. 5,945,459, US 2011/301024 and LEI SHI ET AL: “Studies on surface impregnation combustion method to prepare supported Co/SiO catalysts and its application for Fischer-Tropsch synthesis”, (APPLIED CATALYSIS A: GENERAL, ELSEVIER SCIENCE, AMSTERDAM, NL, vol. 435, 6 Jun. 2012 (2012-06-06), pages 217-224, XP028425865, ISSN: 0926-860X, DOI: 10.1016/J.APCATA.2012.06.007) disclose methods involving impregnation.
Catalysts can be prepared by obtaining a metal hydroxide, carefully oxidising it to the metal oxide and then placing it in the appropriate reactor where it is reduced to the metal in situ.
CN 104 174 400 discloses a method of manufacturing a Fischer-Tropsch catalyst based on impregnating a carrier material.
The first step of the process according to US 2012/083540 entails providing Fe(II) carboxylate in solution. This solution may be formed by means of a dissolution step wherein a source of iron, Fe(0), is dissolved in a suitable solution, preferably an acidic solution, preferably an aqueous solution including one or more carboxylic acids, in order to convert iron in the zero oxidation state to Fe(II) carboxylate in solution where the iron is in an oxidation state of two.
U.S. Pat. No. 5,945,459 discloses a preparation of a catalyst, in which a preformed particulate refractory inorganic solids support is impregnated with a compound, or salt, of a catalytic metal. Similarly, US 2011/301024 discloses a preparation method based on impregnation.
There is a continuous interest in finding catalysts for use in the Fischer-Tropsch synthesis which provide an improved activity and/or an improved selectivity in the conversion of carbon monoxide into valuable hydrocarbons, in particular hydrocarbons containing 5 or more carbon atoms (“C5+ hydrocarbons” hereinafter), and which minimise the formation of methane, which is a hydrocarbon carbon frequently considered as being of lower value.